1. Field of the Invention
The present invention relates to a sheet discharging device, a sheet processing apparatus, an image forming system, and a sheet discharging method, and more particularly concerns a sheet discharging device configured to deliver air to a sheet of a recording medium (hereinafter simply referred to as a “sheet”) such as paper, recording paper, transfer paper, or a transparency when the sheet is discharged to be stacked while being aligned, a sheet processing apparatus that includes the sheet discharging device, an image forming system including the sheet processing apparatus and an image forming apparatus such as a copier, a printer, a facsimile, or a digital multifunction peripheral, and a method implemented by the sheet discharging device.
2. Description of the Related Art
Conventionally, sheet processing apparatuses that perform various processing, e.g., postprocessing such as alignment, stapling, folding, and bookbinding, on sheets ejected from an image forming apparatus are widely known and used. Such a sheet processing apparatus that performs postprocessing is referred to as a sheet postprocessing apparatus below. In recent years, variety of paper that is desired to be processed by sheet postprocessing apparatuses of this type has been noticeably increased. In particular, color image forming apparatuses form images with increasing frequency on coated paper that produces visually-superior images and is commonly used in brochures, leaflets, and the like. Coated paper generally has the following properties.
1) high surface smoothness
2) high inter-sheet clinging force
3) low Clark stiffness
These properties can make coated paper less favorable in terms of sheet stacking.
Apparatuses that use a retainer for holding an ejected sheet(s) at a normal position to prevent unfavorable stacking have already been known. Such an apparatus that employs the retainer can prevent a preceding sheet from being pushed out by a subsequent sheet; however, a thin sheet that is easy to buckle can be buckled by sheet clinging and conveyed in a state of clinging to a preceding sheet. This can result in bending of the sheet. To this end, a technique of additionally providing a blower fan for preventing a sheet ejected onto a tray unit from clinging to a sheet already placed on the tray unit is disclosed (in, for example, Japanese Patent Application Laid-open No. 2011-57313).
The technique disclosed in Japanese Patent Application Laid-open No. 2011-57313 prevents undesirable sheet conveyance and sheet ejection by addition of the blower fan; however, disclosed in the technique is only the addition of the blower fan. More specifically, concrete methods concerning, for example, an airflow rate and a direction of air to be delivered by the blower fan, for preventing sheet clinging or sheet bending resulting from sheet clinging are not disclosed. For this reason, although air blowing is expected to be effective in preventing sheet clinging, it is not certain whether application of the technique to a sheet discharging unit of a sheet postprocessing apparatus can reliably prevent sheet clinging and sheet bending.